Field of the Invention
The present invention relates to a processing system for processing an evaporative fuel emission generated in a fuel tank using a canister during refueling. In particular, the present invention relates to an evaporative fuel emission processing system for a so-called closed or sealed type fuel tank having a shut-off valve provided between the fuel tank and the canister.
Background Information
In order to prevent fuel vapor leaks to the outside, a fuel evaporative emission processing system has been widely known, in which fuel vapor generated in a vehicle fuel tank is temporarily adsorbed in a canister using an adsorbent such as activated carbon, and then, during the operation of the internal combustion engine, through introduction of fresh air to purge the evaporative fuel components from the canister and introduce into an intake system of the internal combustion engine. In addition, in recent years, as disclosed in Japanese Unexamined Patent Application Publication No. 2004-156499 (Patent Document 1), various types of evaporative fuel processing devices have been proposed in which a shut-off valve is provided in a fuel vapor passage connecting the fuel tank and the canister, and essentially by maintaining to close the shut-off valve except for the case of refueling, the fuel tank is maintained in a sealed state.
In the evaporative fuel emission processing system of the sealed type fuel tank having a shut-off valve described above, there is a concern that a pressure in the fuel tank reaches a high pressure value while the shut-off valve is closed. In Patent Document 1, when the tank pressure is high, by opening the shut-off valve during canister purging, reduction in the fuel tank pressure is proposed.
However, in the technique described in Patent Document 1, since the fuel vapor flowing out of the fuel tank when opening the shut-off valve to reduce the pressure in the fuel tank is headed towards the intake passage of the internal combustion engine via the canister, there is a concern that the amount of adsorption in the canister increases substantially. With such a state in which the amount of adsorption in the canister is increased, when performing refueling to a stopped vehicle, the amount of evaporative fuel flowing from the fuel tank into the canister will be too large to be sufficiently adsorbed.